The subject matter described herein relates generally to systems for operating a plurality of wind turbines in a wind farm, and more particularly, to systems for controlling reactive power generated in the wind farm.
Generally, a wind turbine includes a turbine that has a rotor that includes a rotatable hub assembly having multiple blades. The blades transform wind energy into a mechanical rotational torque that drives one or more generators via the rotor. The generators are sometimes, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into a utility grid via at least one electrical connection. Gearless direct drive wind turbines also exist. The rotor, generator, gearbox and other components are typically mounted within a housing, or nacelle, that is positioned on top of a base that may be a truss or tubular tower.
Some wind turbine configurations include double-fed induction generators (DFIGs). Such configurations may also include power converters that are used to convert a frequency of generated electrical power to a frequency substantially similar to a utility grid frequency. Moreover, such converters, in conjunction with the DFIG, also transmit electrical power between the utility grid and the generator as well as transmit generator excitation power to a wound generator rotor from one of the connections to the electrical utility grid connection. Alternatively, some wind turbine configurations include, but are not limited to, alternative types of induction generators, permanent magnet (PM) synchronous generators and electrically-excited synchronous generators and switched reluctance generators. These alternative configurations may also include power converters that are used to convert the frequencies as described above and transmit electrical power between the utility grid and the generator.
Known wind turbines have a plurality of mechanical and electrical components. Each electrical and/or mechanical component may have independent or different operating limitations, such as current, voltage, power, and/or temperature limits, than other components. Moreover, known wind turbines typically are designed and/or assembled with predefined rated power limits. To operate within such rated power limits, the electrical and/or mechanical components may be operated with large margins for the operating limitations. Such operation may result in inefficient wind turbine operation, and a power generation capability of the wind turbine may be underutilized.
When a plurality of wind turbines are arranged in a wind farm, reactive power generated by individual wind turbines may be different. In particular, an increasing size of wind farms results in an increasing area for the wind farm such that the difference in reactive power production, e.g. due to difference in topology increases as well. As an adjustable power factor PF is desired, such as a power factor of one (PF=1), controlling a large number of wind turbines with the identical or nearly identical commands for compensating reactive power is not efficient. The larger the wind farm, the wider the area for the installation of individual wind turbines is. Thus, long electrical connections between individual wind turbines and an electrical collector bar for collecting the energy provided by the individual wind turbines is an issue. Therefore, an efficient and cost-effective power control for wind turbines arranged in a wind farm is desired.